linux-kernel - Re: A MMC card transfer issue

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Date:	Tue, 9 Nov 2010 16:29:34 +0900
From:	"Tomoya MORINAGA" <tomoya-linux@....okisemi.com>
To:	"Kyungmin Park" <kmpark@...radead.org>
Cc:	<linux-mmc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	"Andrew\"" <andrew.chih.howe.khor@...el.com>,
	<kok.howg.ewe@...el.com>
Subject: Re: A MMC card transfer issue

Hi Park,

Thank you for your information.
I will try it soon.

Thanks,
Tomoya MORINAGA
OKI SEMICONDUCTOR CO., LTD.
----- Original Message ----- 
From: "Kyungmin Park" <kmpark@...radead.org>
To: "Tomoya MORINAGA" <tomoya-linux@....okisemi.com>
Cc: <linux-mmc@...r.kernel.org>; <linux-kernel@...r.kernel.org>; "Andrew"" <andrew.chih.howe.khor@...el.com>;
<kok.howg.ewe@...el.com>
Sent: Tuesday, November 09, 2010 2:53 PM
Subject: Re: A MMC card transfer issue


> 2010/11/9 Tomoya MORINAGA <tomoya-linux@....okisemi.com>:
> > I am facing the issue about some MMC cards on Intel EG20T PCH (Platform Controller Hub).
> > The linux version is 2.6.36.
> > I can not transfer data the MMC cards (e.g. Transcned MMC card).
> > The card is 1 bit bus width. And the card is according to MMC specification V3.x.
> > And the EG20T has a 4 bit bus width capability
> > Linux MMC standard driver decides the card bus width as 4 bit,
> > if the MMC specification version is larger than or equal to V4.0 like below.
> >
> > linux/drivers/mmc/core/mmc.c
> >
> > 505 /*
> > 506 * Activate wide bus (if supported).
> > 507 */
> > 508 if ((card->csd.mmca_vsn >= CSD_SPEC_VER_4) &&
> > 509 (host->caps & (MMC_CAP_4_BIT_DATA | MMC_CAP_8_BIT_DATA))) {
> > 510 unsigned ext_csd_bit, bus_width;
> > 511
> > 512 if (host->caps & MMC_CAP_8_BIT_DATA) {
> > 513 ext_csd_bit = EXT_CSD_BUS_WIDTH_8;
> > 514 bus_width = MMC_BUS_WIDTH_8;
> > 515 } else {
> > 516 ext_csd_bit = EXT_CSD_BUS_WIDTH_4;
> > 517 bus_width = MMC_BUS_WIDTH_4;
> > 518 }
> > 519
> > 520 err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
> > 521 EXT_CSD_BUS_WIDTH, ext_csd_bit);
> > 522
> > 523 if (err && err != -EBADMSG)
> > 524 goto free_card;
> > 525
> > 526 if (err) {
> > 527 printk(KERN_WARNING "%s: switch to bus width %d "
> > 528 "failed\n", mmc_hostname(card->host),
> > 529 1 << bus_width);
> > 530 err = 0;
> > 531 } else {
> > 532 mmc_set_bus_width(card->host, bus_width);
> > 533 }
> > 534 }
> > 535
> >
> > However the MMC specification version id is the same as V3.x and V4.0.
> > Therefore the driver uses the 4 bit bus width for the MMC card
> > even if the card has only 1 bit bus width.
> > I modified the driver to use 1 bit bus width only tentatively and confirmed that
> > we can mount the card and R/W correctly.
> >
> > I think we can not support MMC_CAP_4_BIT_DATA or MMC_CAP_8_BIT_DATA in MMC V4.0.
> >
> > How do you think ?
>
> You can find a patch for 4-bit support. the problem is there's some
> bug related so it set the 4 & 8 bit support both.
> So line 512 is always true. you can just remove the one line like this.
>
> It's quirk-and-dirty patch. now we try to find a generic solution to
> solve this issue.
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -1849,7 +1849,7 @@ int sdhci_add_host(struct sdhci_host *host)
>         mmc->caps |= MMC_CAP_SDIO_IRQ;
>
>         if (!(host->quirks & SDHCI_QUIRK_FORCE_1_BIT_DATA))
> -               mmc->caps |= MMC_CAP_4_BIT_DATA | MMC_CAP_8_BIT_DATA;
> +               mmc->caps |= MMC_CAP_4_BIT_DATA;
>
>         if (caps & SDHCI_CAN_DO_HISPD)
>                 mmc->caps |= MMC_CAP_SD_HIGHSPEED | MMC_CAP_MMC_HIGHSPEED;
>
> Thank you,
> Kyungmin Park
> >
> > --
> > Thanks,
> > Tomoya MORINAGA(OKI SEMICONDUCTOR CO., LTD.)
> > --
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> >
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